1. Field of the Invention
The present invention relates to a sequence control unit, a driving method thereof, and a liquid crystal display device having the same. The present invention is suitable for a wide scope of applications, including outputting a voltage with a delay time after the voltage is input.
2. Discussion of the Background
Generally, a liquid crystal display (“LCD”) device includes an LCD panel for displaying an image, a driving circuit unit for driving the LCD panel, and a backlight unit for generating light to display an image on the LCD panel.
The LCD panel includes a thin film transistor (“TFT”) substrate, a color filter substrate opposing the TFT substrate, and liquid crystals interposed between the TFT substrate and the color filter substrate. The LCD panel displays an image by adjusting light transmissivity through the liquid crystals in response to a potential difference between a pixel electrode arranged on the TFT substrate and a common electrode arranged on the color filter substrate.
A panel driving unit includes a gate driving unit for driving a gate line included in the LCD panel, a data driving unit for driving a data line included in the LCD panel, a timing controller for supplying a gate control signal to the gate driving unit and a data control signal to the data driving unit, and a direct current/direct current converter (“DC/DC converter”) for supplying driving voltages to the data driving unit and the common electrode. In this case, the driving voltages supplied from the DC/DC converter may be output to the corresponding data driving unit or the common electrode with a predetermined time delay or in a preset sequence. The LCD device conventionally uses a resistance-capacitance (“RC”) delay circuit to control the time delay of the driving voltages supplied to the corresponding driving units.
FIG. 1A is a diagram of an RC delay circuit of an LCD device according to the prior art. FIG. 1B is a diagram illustrating sequence control using an RC delay circuit of an LCD device according to the prior art.
Referring to FIG. 1A, a conventional LCD device uses an RC delay circuit having a resistor R connected in parallel with a capacitor C to control a sequence of driving voltages Vin. A second terminal of the capacitor C is connected to ground.
The RC delay circuit delays the output of an output voltage Vout after the input of a driving voltage Vin according to an RC value. In this case, a waveform of the input driving voltage Vin via the RC delay circuit, as shown in FIG. 1B, is delayed by a delay time T1. The input driving voltage Vin passing through the RC delay circuit reaches a threshold voltage Vth along a smooth curve and then reaches a turn-on voltage Vton. If the delay time T1 is measured from the input driving voltage Vin to the threshold voltage Vth, the delay time T1 may vary according to values of the resistor R and capacitor C of the RC delay circuit.
In the LCD device, the actual delay time may vary according to lengths of signal lines supplied to the respective driving units and a delay caused by a parasitic capacitance between adjacent signal lines. Thus, the delay time T1 taken for the input driving voltage Vin to reach the threshold voltage Vth may vary according to environmental conditions of the LCD device. If the delay time T1 of the RC delay circuit increases, a rising time of the input driving voltage Vin increases. Accordingly, a signal-to-noise ratio (“SNR”) at the data driving unit receiving the corresponding driving voltage may decrease. If the SNR decreases, the data driving unit may have difficulty recognizing the corresponding driving voltage, thereby generating an error. Moreover, if the delay time T1 of the input driving voltage Vin increases, it may be difficult to match the timings of the driving voltages Vin actually outputted from the respective driving units of the LCD device. So, a driving failure of the LCD device may occur.